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Author: Patrick Mineault | Website:

The curveTo command

We'll need the following drawing API commands for this movie:


The first three were covered in the first tutorial so that leaves us with curveTo. The curveTo(controlX, controlY, endX, endY) command draws a quadratic curve from (startX, startY) to (endX, endY). The (startX, startY) point is determined by the last point used by a moveTo, lineTo or curveTo command. The (controlX, controlY) point acts as a control point for the curve. The control point constrains the slope at the two end points of the curve. You can think of the control point as a 'magnetic point' to which the curve is attracted to. It works much like the control points on a Bezier curve, except there's one one per curve instead of two.

Getting back to our movie, the mask for the pics will be created in three successive stages, which are shown in the following diagram:

As you see, the mask will consist at first of a line at the top and will morph into the 4 sided-figure delimited by the blue line and the exterior frame. This will then morph into the red outline figure and finally into a complete rectangle. The crosses represent the approximate locations of the control points of the blue and red lines. We see immediately from this diagram that all of our figures can be represented by a four-sided figure with three straight sides and a curved line at the bottom.

One thing you may have noticed is that for the first and last frames the bottom line will not be curved. In this case the control point may be placed anywhere on the straight line. This will give us some flexibility in animation as you will see later on.

» Level Advanced

Added: 2004-06-01
Rating: 8 Votes: 12
(10 being the highest)
» Author
The author is a math enthusiast. He nows studies Physics at McGill University.
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